title: A comparison of impedance and electromyogram measurements in detecting the presence of pedicle wall breakthrough.
abstract: METHODS
  A prospective comparison of impedance measurements, electrically elicited electromyograms, and mechanically elicited electromyograms to detect pedicle wall breakthrough.
  
  
  OBJECTIVE
  To determine whether impedance measurements are as sensitive as electromyogram measurements in evaluating pedicle wall breakthrough.
  
  
  BACKGROUND
  In a previous animal study, impedance values in pedicle screw placement were tested, to determine a baseline value for an intact pedicle. If pedicle wall breakthrough occurred, it was thought that the impedance values should be significantly lower.
  
  
  METHODS
  Impedance measurements, electrically elicited electromyograms and mechanically elicited electromyograms were recorded in 20 patients undergoing surgery for spinal degeneration, using previously described standard protocol. Analysis of variance statistics were used to evaluate the data.
  
  
  RESULTS
  Impedance values for the pedicle holes varied from 500 ohms to 31,000 ohms. There was no correlation between these values and those of the two pedicles in which breaches were detected on visual inspection. Electrically elicited electromyograms detected the breakthroughs in both pedicles, whereas mechanically elicited electromyograms detected one of the breakthroughs.
  
  
  CONCLUSIONS
  Electrically elicited electromyograms were more sensitive in detecting pedicle wall breakthrough than were impedance measurements. This may be because of the inability to ascribe absolute impedance values to human pedicle bone caused by the wide variability in bone quality.
authors.affiliation: Charlotte Spine Center, North Carolina, USA.
authors.forename: B V
authors.initials: BV
authors.lastname: Darden
authors.forename: J H
authors.initials: JH
authors.lastname: Owen
authors.forename: M K
authors.initials: MK
authors.lastname: Hatley
authors.forename: J
authors.initials: J
authors.lastname: Kostuik
authors.forename: S M
authors.initials: SM
authors.lastname: Tooke
mesh_terms: D000328:Adult; D000368:Aged; D001863:Bone Screws / Q000009:adverse effects*; D017097:Electric Impedance; D004568:Electrodiagnosis; D004576:Electromyography; D005260:Female; D006801:Humans; D007431:Intraoperative Complications / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D013131:Spine / Q000601:surgery*